1. Field of the Invention
The present invention relates to a laser module for a bar code reader, which includes a light emitting element and a light projection lens and irradiates an emitted beam to a bar code being an irradiation target and, more particularly, to a technique for improving a lens holder for holding the light projection lens.
2. Description of Related Art
In recent years, many shops and factories and the like carry out sales management of goods and manufacture management of products and the like by putting a bar code indicative of digital information on an article and optically scanning it and thereby reading the information. Typically, lights are irradiated to the bar code of this kind, and a magnitude of reflection light is converted from an optical signal to an electric signal. Then, the information is read from a combination of detected signals.
As an apparatus for carrying out such optically reading operation as mentioned above, for example, there is a bar code reader having a mechanism shown in FIG. 7 in a main body. This bar code reader includes a light emitter/receiver 1 and a movable mirror 3 in a main portion of the configuration. The light emitter/receiver 1 is configured such that a laser module 5 and a light receiving module 7 are mounted on a substrate 9.
The laser module 5 further includes a light emitting element 11, a housing 13 and a lens holder 15. The lens holder 15 has a slit 17 at one end of a cylinder. Inside the lens holder 15, a retainer 21 fixedly holds a light projection lens 19. Also, the light receiving module 7 has a light receiving element 23, a housing 25, a light receiving lens 27 and a band pass filter (BPF) 29. The band pass filter 29 is operated so as to avoid receiving unnecessary lights other than the light at a light emitting frequency, in order to improve a reading accuracy.
A mirror 33 of the movable mirror 3 is oscillated in order to irradiate lights to the entire region of a bar code (not shown) that is an irradiation target. That is. a magnet (not shown) is fixed to the mirror 33 that is oscillatably supported with a pivot as a center. Then, the magnet is inserted into a driving coil (not shown), and a positive current and a negative current are alternatively applied to the driving coil, for example, at a constant cycle. Thus, the magnet is attracted into and repelled from the driving coil. Hence, the mirror 33 oscillates around the pivot as a support shaft.
In this bar code reader, the lights emitted from the light emitting element 11 are focused by the light projection lens 19. Then, those lights reflect off the mirror 33 of the movable mirror 3 and irradiate the entire region of the bar code.
On the other hand, although the lights irradiated to a surface of the bar code are diffusedly reflected, they are again returned back to the mirror 33 after the change in an optical amount resulting from white and black components of the bar code. Then, the light receiving lens 27 collects thus-reflected lights. In the light receiving element 23, the change in the optical amount is electrically converted and outputted. This output signal is processed by a computer (not shown). Hence, it is possible to decode the information of the bar code.
By the way, in the laser module, in order to improve an optical accuracy, it is necessary to position the light receiving element and the lens holder at high accuracies. For this reason, conventionally, the positioning is adjusted by preliminarily fixing the light emitting element to one end of the housing and moving the lens holder in a direction of a central axis at the other end of the housing. Then, at an optimal position, a laser welding is carried out to weld and to fix the lens holder and the housing. From the above-mentioned reasons, an Austenitic stainless steel SUS304, which is a metal having good weldability and having excellent corrosion and heat resistivity, and the like are used for the lens holder.
However, the SUS304 is poor in machinability although it is superior in weldability. On the other hand, on the lens holder, it is necessary to form the slit 17 shown in FIG. 9 for outputting the lights passed through the light projection lens and a retaining stage 15a of the light projection lens shown in FIG. 8 by a cutting operation. For this reason, the cutting operation is performed on the lens holder composed of the SUS304 having poor machinability. Thus, it is difficult to carry out a machining operation at high accuracy. Also, a burr 40 is easily induced. If the burr 40 is protruded into an optical path after the laser module is assembled or if this burr 40 is dropped, it has a bad influence on a beam property (especially if the burr exists in the slit portion) and causes the quality defect such as deterioration in reading accuracy or the like. Hence, in a case of the conventional laser module, after the cutting operation of the lens holder, a second operation, such as deburring and the like, and a burr removal checking operation using a microscope must be performed on all products. Moreover, the conventional laser module is low in productivity as well as poor in yield at the same time. Hence, this has a problem of an increase in a manufacturing cost.